Traditionally fuel injectors have consisted of a power group and a valve group. The power group has a fuel inlet tube/pole, a magnetic coil, and a housing. The main function of the housing has been to serve as a magnetic flux return path for the coil. However, additional functions of the housing include: maintaining injector shape even under compression/installation force; forming a structural bridge between components such as the inlet tube and valve body by attachment to such components, such as by crimping for example; aligning the inlet tube to the armature face; providing electrical coil terminal passage, typically in the form of two circular holes in the housing through which respective terminals pass from the coil to an external electrical connector; and forming a hermetic surface for O-ring sealing. This has led to a rather complicated housing shape with tight tolerances, basically dictating that the housing be manufactured from thick, machined solid metal or powdered metal.
A trend for down-sizing engine compartments has forced components to become smaller, and one area of size reduction has been the injector outer diameter. Smaller outer diameter injectors still require maintaining the same inlet tube outer diameter (for standard size O-ring usage in sealing to a fuel rail socket), and this makes it difficult to create a single standard electrical terminal passage through the wall of a typical housing.
Additionally, the traditional housing is typically greater than two millimeters in thickness so that maintaining this thickness while trying to down-size the outer diameter can result in performance loss since room for the coil must necessarily decrease.
New structural solutions for alignment and attachment of the power group components, in addition to different hermetic sealing concepts have led to less strict demands on the housing. Designs that have taken advantage of minimal housing design requirements by utilizing strap or frame concepts for a housing, although low in cost and easy to manufacture, limit the cross-sectional area required for magnetic flux path; structural/installation force deflection requirements are still present; because the straps or frames do not cover the entire 360 degrees, they must be thicker, resulting in a minimal reduction in injector outer diameter. Additionally, the structural integrity of the power group can shift due to the components being exposed to the pressure of the overmold material injected during the overmold process to encapsulate the coil and housing.
Other concepts have included processing flat sheets of metal 1 to 1.5 mm thick for housings. This has helped in minimizing component shift during overmold, but at the disadvantage of requiring two individual passages for electrical terminals due to terminal passage geometry requirements. This requires two additional components and a weld or solder joint.
The present invention relates to a low cost, thinner walled housing for an injector power group and several manufacturing methods to accomplish this shape. This results in reduced injector outer diameter, limits components exposure to high overmolding pressures, and hence limits component shift caused by the overmolding operation, and has a geometry conducive to electrical terminal blade passage.
Various features, advantages and the inventive aspects will be seen in the ensuing description and claims which are accompanied by drawings that disclose a presently preferred exemplary embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.